1. Field of the Invention
The present invention relates to an injection member attachment structure for an injection molding machine.
2. Description of the Related Art
In a general in-line type injection molding machine, a screw having a spiral groove is disposed inside a heating cylinder so as to be used as a member that feeds resin into a mold, a pellet-shaped resin material is fed into the heating cylinder, the resin material is melted and measured by the rotation and the backward movement of the screw, and the molten resin is injected into the mold by the forward movement of the screw so as to perform a molding process.
For that reason, the screw is attached to the injection molding machine so as to transmit the rotational power and the forward/backward moving power. Due to the rotation and the forward/backward movement of the screw, the rotational power is transmitted to the screw by a key groove or a spline. Due to the forward/backward movement of the screw, the power is mainly transmitted in the screw retracting direction by the key groove or the flange. Further, the power is transmitted in the screw advancing direction when the rear end surface of the screw is pressed by an injection shaft during the injection.
In a recent molding machine, parts are decreased in thickness, and a high injection pressure is demanded during a molding process. Accordingly, an injection operation is performed at a high injection force. However, when the injection force of the injection operation is increased, the rear end surface of the screw is pressed by a large force during the injection operation. Accordingly, a large load is applied to the rear end surface of the screw and a pressing surface of the injection shaft pressing the screw.
When such a large load is repeatedly applied to the screw due to the injection operation, there is concern that plastic deformation will occur in the rear end surface of the screw or sink tracing will occur in the pressing surface of the injection shaft. The plastic deformation or the sink tracing is called permanent strain. When the permanent strain occurs, rattling which is not expected in design occurs. Thus, there is concern that the molding controllability is degraded or the part is damaged. For that reason, it is desirable to decrease the load applied to the rear end surface of the screw as small as possible during the injection operation.
As a technique of decreasing the load applied to the rear end surface of the screw or the pressing surface of the injection shaft, there is known a technique of increasing a contact area between the rear end surface of the screw and the pressing surface of the injection shaft by increasing the size of the rear end surface of the screw. However, when the outer diameter of the rear end surface of the screw is set to be larger than the inner diameter of the heating cylinder of the molding machine, the screw is extracted from the inside of the heating cylinder during the maintenance only in the backward direction since the maintenance is performed by separating the screw from the injection molding machine, and hence the maintenance workability is degraded.
In order to prevent degradation in maintenance workability, the outer diameter of the rear end surface of the screw needs to be equal to or smaller than the inner diameter of the heating cylinder. Thus, there is a physical limit in the technique of increasing the contact area between the rear end surface of the screw and the pressing surface of the injection shaft.
Another technique of preventing the permanent strain in the rear end surface of the screw or the pressing surface of the injection shaft is disclosed, for example, in the following three patent documents.
JP 2010-58275 A discloses a technique of increasing the diameter of a pressure receiving surface pressed in a screw of an injection molding machine and providing a spacer between the pressure receiving surface of a rear end of a screw and a spline.
JP 2003-211490 A discloses a technique of providing a spacer between a rear end surface of a screw and a sleeve.
JP 3-23420 Y discloses a technique of providing an intermediate member between a rear end surface of a screw and an injection shim.
However, in the techniques disclosed in the above-described three patent documents, the spacer or the intermediate member is provided, but a member for fixing the spacer or the intermediate member is not disclosed.
For that reason, in the related art, when the permanent strain occurs in the spacer or the intermediate member, the rattling of the spacer or the intermediate member or the uneven contact thereof occurs so that the permanent strain or the breakage of the spacer or the intermediate member is promoted or seizure inside the injection shaft sleeve occurs. Accordingly, there is concern that the spacer or the intermediate member may not be detached from the injection shaft sleeve.
Further, there is concern that the spacer or the intermediate member will come off from the injection shaft sleeve when the screw is detached for the maintenance and hence an operator or a peripheral object is be damaged.